1. Field of the Invention
This invention relates in general to heat exchangers and in particular to an apparatus for heating liquid by use of either a liquid or a vapor.
2. Description of the Prior Art
Liquids have been heated by fluids such as steam or other hot liquids in various manners. It is known that heat transfer coefficients and the efficiency of the heat exchanger improve with the velocity of the fluids. One type of heat exchanger employing high flow rates uses concentric pipes. The cold liquid is forced through the inner pipe while steam is forced through the annular space. Heat is transferred from the steam through the walls of the inner pipe. However the heat transferred to the outer pipe walls is lost, since the liquid to be cooled is located only in the interior pipe.
In U.S. Pat. No. 403,123, a steam water heater is disclosed that uses a bundle of concentric tubes in a tank. Cold water flows up through the annular passage of some of the tube pairs and down the annular passages of others. Some of the steam flows up the inner tubes, while the remainder passes exterior of the outer tubes and out the top of the tank. The velocity of flow is reduced in the resultingly large steam flow areas. In addition, a portion of the steam flows over the cold water intake at a point where thermal stresses and expansion cannot be easily alleviated.